Inverter system with resonant electro-dynamical device

ABSTRACT

This invention combines a resonant electrodynamical device with an electromagnetic oscillator that has its period of oscillation syntonized with the natural period of oscillation of the resonant electrodynamical device. In the preferred embodiment, the resonant electrodynamical device is a swing motor connected with a compressor load, and power for driving the swing motor is supplied by the syntonic oscillator. A feedback from the swing motor maintains the oscillator in syntonization with the natural period of oscillation of the swing motor.

United States Patent Thomas, Jr. et al.

[54] INVERTER SYSTEM WITH RESONANT ELECTRO-DYNAMICAL DEVICE [72] Inventors: John A. Thomas, Jr.; Gerhard D. Span- [2l] Appl. No.: 19,223

............................... ..4l7/417,3l8/l27 3,118,383 1/1964 Woodward... 2,997,584 8/l96l Querfunh.....

..4l7/417 X ..336/l55 X Primary Examiner-Robert M. Walker Attorney-Sandoe, Hopgood & Calimafde [57] ABSTRACT This invention combines a resonant electrodynamical device with an electromagnetic oscillator that has its period of oscillation syntonized with the natural period of oscillation of the resonant electrodynamical device. In the preferred embodi- [52] US. Cl... ment, the resonant electrodynamical device is a swing motor [5 l] lnt..Cl. ..F04b 35/04, F04b 17/04, H02b 3/00 connected with a compressor load, and power for driving the [58] Field of Search 417/416, 417, 418, 424; swing motor is supplied by the syntonic oscillator. A feedback 313 127, 123, 129; 321 34 44 49; 33 5 5 from the swing motor maintains the oscillator in syntonization 1 v with the natural period of oscillation of the swing motor. [56] References cued 13 Claims, 5 Drawing Figures UNITED STATES PATENTS 3,447,051 5/1969 Attwood m ..s1s/1z7 IO s 2 r SWING "d fi c PRESS R INVERTER MOTOR CM 0 Patented May 2,1 72 3,659,968-

FIG. 1. 26 7g INVERTER "6 j g 'gg 'ZCOMPRESSOR F 3 1 v I0 l4 l5 20 I 82 v FIG 2 R R k V/ 84 1190 I 94 y swms MOTOR -92 88 3 +94 TRANSFORMER 3 i 5 no I03 2 3 -10! I020 a j 0 Q -II2 j-II8 I04 z a SATURATING 5w CORE -I6- ELECTRO- 3 f TRANSFORMER DYNAMIC 1 355 1 4 LOAD :5: SE] r p sw m?- I 9 A z OSCILLA'IDRY a T DEVICE 2' V ORS IN N ATTORNEYS.

BACKGROUND AND SUMMARY OF THE INVENTION In its broadest aspects, this invention includes an electromagnetic oscillator with a period of oscillation which is in syntonization with the natural-period of oscillation of a resonant electrodynamic device. When the resonant electrodynamic device is a load to which the oscillator supplies power, the syntonized relationship results in more efficient operation.

In the preferred embodiment of the invention, the load is a swing motor with a natural period of oscillation, and self-induced current of the swing motor is-used as a feedback to the electromagnetic oscillator to maintain syntonization. Connection of the motor with its power supply is inductive, thus providing a safety that can not be obtained with motors which are directly connected to their power supply. The inductive coupling is made through a saturating core transformer that controls the period of the electromagnetic oscillator; and the point of flux saturation of the transformer in time is controlled by self-generated currents of the'resonant electrodynamic device. The invention can use an oscillator powered from a unidirectional or a bi-directional power source; and can supply uni-directional current while being powered by a bidirectional power source and at the same time driving the clectrodynamic device.

The invention will be described with an oscillator having a transformer used to control the electronic action of two transistors for the purpose of power amplification and power inversion and for supplying alternating current of syntonized frequency to a frequency sensitive load comprising a swing motor; which motor is representative of frequency-sensitive loads.

A swing motor is an electrodynamical reciprocating device similar in principle to the electromagnetic speaker commonly used in radios and .high-fidelityequipment. The swing motor can be connected to the piston of a compressor and such a combination provides a low-cost, altemating-current power operated compressor for apparatus such as mechanical refrigerators, and obtains high reliability and high efficiency.

'The compressor piston is connected to a swing motor coil suspended by springs in a gap of an electromagnet. Upon the application of alternating-current power, the coil and the piston vibrate and produce a reciprocating motion for the compressor piston. By having the mechanical resonance of the coil and springs substantially the same as that of the frequency of the power supply to the motor, a high efi'rciency is obtained.

Swing motor-operated compressors are well known, and this invention is an improvement on the known systems that have such motor-operated compressors. This invention combines a swing motor with an oscillator that serves as an inverter that has a frequency syntonized with that of the swing motor. When this invention is in operation, the swing motor switches the inverter at the swing motor frequency and by doing so, reduces the current drawn and the transformer losses in the inverter so that high efficiency is obtained. This is particularly important when the source of power'is a storage battery because the apparatus can be operated for a longer time from the battery, or a battery of smaller capacity and lower cost can be used.

This invention has lower manufacturing costs and lower operating costs than swing motor systems of the prior art; and has high-volume output, high reliability, electrical efliciency of 90'percent and higher, frequency syntonization, and alternating-current or direct-current operation.

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

BRIEF DESCRIPTION or DRAWING In the drawing, ,forming apart hereof, in which like reference characters indicate corresponding parts in all the views: I I

FIG. 1 is a diagramrnatic illustrationof the combination of an electromagnetic oscillator comprising an inverterconnected with a swing motor which drives acornpressor, and with the invertersupplied selectively with either direct of alternating current; FIG." 2 is a wiring diagram for thesystem shown diagrammatically in FIG. 1;

FIG. 3 a sectional view of the swing motor shown diagrammatically in FIGS. 1 and 2; and

FIGS. 4 and 5 are wiring diagrams for modified forms of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 shows a swing motor 10 connected with an inverter 12 which supplies power to the motor. The inverter 12 can be supplied with power through conductors 14 and 15 leading to a switch 16. .When the switch 16 is closed toward the left, it is connected through a bridge circuit 17 to an alternating current supply source 18. When the switch 16 is closed toward the right, direct current power from a battery 20 is supplied to the inverter 12.

FIG. 2 shows a wiring diagram for the inverter l2.lt includes a transformer 30 having a ferrousmetal core 32 which is preferably made of steel, such as used in power transformers, and it includes three The'first winding 34 is a collector winding or direct current, primary winding which has a center tap or terminal 36 and other terminals 38 and 39 at its opposite ends.

The transformer 30 also has a drive winding 40 with a center tap or terminal 42 and opposite end terminals 44 and 46. This drive winding 40 is for the purpose of operating switching elements which will be described.

' The transformer 30 also has a loa Winding 50 with end terminals connected to the swing motor 10 by conductors 52 and 54. In order to make the electromagnetic oscillator, whether or not illustrated as inverter 12, capable of operating also with alternating current from the alternating-current supply 18, the electrical circuit has a bridge 17 connected across the alternating current supply 18 with diodes 55, in each leg of the bridge" 17, the inverter 12 is supplied with a unidirectional but pulsating current from the alternating current supply 18. A capacitor56 is connected across the diodes 55 so as to supply a starting current and to prevent the pulsating current from becoming less than is required for proper switching action of transistors 62 and 64. Thus, with an alternating current from the supply 18, the inverter 12 is supplied with a unidirectional pulsating current.

For purposes of invention,- the bridge 17 and capacitor 56 are to be considered part of the inverter and-it is to be understood that the term inverter" is used to designate a device that changes current of one frequency to another or that changes direct or pulsating current to altemating current or alternating current to direct current. As used herein, the inverter 12 changes direct current from the battery 20 into alternating current for'the swingmotor l0 and also changes alternating current from the altematingcurrent source 18 to alternating current of a diflerent frequency for use in the swing motor 10.

Referring again to FIG. 2, a transistor 62 is connected with the tenninal 38 of the primary winding 34; and a second transistor 64 is connected with the terminal 39 of the primary winding 34. These transistors 62 and 64 have corresponding terminals connected with the opposite ends of the winding 34 and the other terminals of the transistors 62 and 64 have a common return through aconductor 66.

The transistor 62 has its base connected to the terminal 46 of the drive winding 40, and the base of the transistor 64 is connected to the opposite terminal 44 of the drive winding 40. The center tap 42 of the drive winding 40 is connected to a common return through a resistor 70. There are capacitors 72 and 74 connected to the bases of transistors 62 and 64,'respectively, and terminations at the center tap 36 of the winding 34.

When the operation of the system is started, using direct current, and the transistor 62 starts to conduct, the voltage developed acrossthe primary winding 34 induces voltage in the base drive winding 40 to drive the transistor 62 rapidly into saturation. Constant voltage is applied to the half of the winding 34 for which the circuit is closed until core saturation is reached. Then the rate of change of flux will drop to zero, the induced voltage first decreasing in value and then becoming zero. This removes the base drive from the transistor 62. The flux begins to decrease and causes the current to build up in the opposite direction. A voltage of opposite polarity is induced in the windings and the transistor 64 begins to conduct. The cycle is then repeated.

In order to start the movement of the resonant spring of the swing motor, a high-energy pulse is required. The transistors 62 and 64 operate in a high forced beta condition. When the swing motor is started, its spring is compressed as the peak current of the first half cycle is attained. The self-generated current of the swing motor is conducted in the load winding 50. Since the load winding 50 is the inductive coupling of the swing motor to the power supply through the transformer, this self-generated current in the load winding causes the rate of change of flux in the transformer to decrease to zero. The transistor 64 is driven on as the transistor 62 is driven off.

As the transistor 64 is driven into saturation, the transistor 62 will receive a reverse bias from the drive winding 64. When this action occurs, a cycle is completed. Thus the resonant frequency of the swing motor (load) switches the inverter 12 at the same frequency. A conventional inverter of this type does not have frequency regulation and the frequency of operation of the inverter is directly proportional to the input voltage to the inverter, when not switched by self-generated currents from the swing motor.

FIG. 3 shows the construction of the swing motor 10. It includes a sealed housing 80. Within this housing there is a yoke 82 to which is connected a permanent magnet84. The magnet 84 can be connected to the yoke 82 in various ways and the illustrated construction has a bolt 86 extending through a pole piece 88 of the magnet and through the upper end of the yoke 82.

The yoke 82 is part of the magnetic circuit and it includes an annular end portion 90 which surrounds the cylindrical pole piece 88 with a gap 92 in which a coil 94 of the swing motor is located.

When current flows in one direction in the coil 94, the coil moves upward in the flux field .which extends across the gap 92. Conversely, when the current flows in the opposite direction in the coil 94, the coil moves downward in the flux field in the gap 92. The coil 94 is connected, at its lower end, to a flange 96 which moves up and down as a unit with the coil 94. The switch motor has resonant spring means including a spring 98 which extends into a recess 100 in the pole piece 88 and which bears against the flange 96 at the lower end of the spring 98. The resonant spring means also includes another spring 101 which has its lower end held in a spring retainer 102 secured to a relatively fixed structure 104. The upper end of the spring 102 fits around a retainer 103 which is a part of a unitary assembly with the flange 96. In describing the operation of the swing motor, the spring 98 will be described as the upper" and the spring 101 will be described as the lower spring, though the swing motor can be made with a single spring which projects through the flange assembly and which is rigidly secured to the part of the flange assembly through which it passes.

The fixed structure 104 is connected with the yoke 82 by columns 106 which include screws and these columns hold the fixed structure 104 in a fixed relation to the yoke 82, though the combined structure preferably has a floating mounting in the housing 80.

A piston 110 is fixed to the flange 96 and extends into a cylinder 112 in the structure 104. An exhaust valve 114 at the lower end of the cylinder 112 is urged toward closed position by a valve spring 116. An intake valve 118 is located in the piston 110.

As the piston 110 is reciprocated up and down in the cylinder 112, gas enters the cylinder through the intake valve 118 and is discharged into the housing which serves as a tank for the compressed gas. The passages by which the gas reaches the cylinder through the intake valve 118 are not all shown in the plane of section of FIG. 3 and since the compressor and its connections are not part of this invention, no further illustration of them is necessary for a complete understanding of this invention.

It is sufficient to understand that the compressor is operated by the reciprocating movement of the flange 96 to which the piston is connected; and this reciprocating movement is obtained by alternately reversing the direction of flow of curand lower springs which alternately compress and expand as the flange 96 reciprocates, there is a natural frequency of oscillation of the flange 96 under the influence of the upper and lower portrons of the spring means. Swing motors are designed for a particular frequency of power supply and thus the springs and the masses of the structure that reciprocates with the springs are selected so that the natural frequency of the springs and their connected structure is nearly equal to the frequency of the power supply with which the swing motor is intended to be used, or slightly greater than the no-load frequency of the inverter.

FIG. 4 is a diagram showing the invention in its most basic concept, and the principles and equations for its operation can be best explained in connection with this figure. The wiring diagram is a simplified version of FIG. 2 with the transistors Q and Q, in place of the transistors 62 and 64, respectively. Power is supplied from an altemating-current generator 18' through a bridge 17 at a voltage E as with corresponding elements of F IG. 1.

Upon application of power, Q ing on the hfe (gain) of Q or Q, and the magnetic state of the transformer. When Q, starts conducting current, 1', establishes an increasing magnetic field in the transformer core which, in turn, induces a current in all secondary coils on the same core. One secondary is connected to the base of Q, and the emitter of Q, through R,. This secondary is the base drive winding. The current I, from the base drive winding regenerates the initial conducting action of 0 until the transistor is fully saturated. At this time, the entire DC source voltage minus the collector to emitter saturation voltage, is applied across the transformer primary.

e voltage acros primary E voltage across power source V voltage across transistor in saturation or 0 will conduct depend- The voltage causes current i, to continue flowing. The current 1', flowing through the primary winding produces a magnetizing force H.

H magnetizing force 1', current flowing through the coil N number of turns in the coil This magnetizing force H produces a flux density B in the iron core depending upon the permeability u of the core material.

B= uH B flux density u permeability H magnetizing force drive windings, thus sustaining the saturated condition of 0,. Upon achieving a certain magnetizing force which is dependent on the material used, the permeability of the transformer core decreases and causes the rate of change of flux density to increase at a much'lesser rate. This results in a drop in the base current 1,, to transistor Q,.,But at the same time the collector current of 0,, L; continues't'o increase and is still supplying magnetizing force as it did when it originally turned on. The continual increase in collector current and sudden decrease in base current, forces the transistor to go out of saturation, because insufiicient base current is available to sustain the collector current as governed by the dc transfer ratio (hfe) of the transistor I collector current I, base current hfe DC forward current transfer ratio As the transistor is forced out of saturation, the emitter to collector voltage increases (V and according to Equation 1 reduces the voltage e across the transformer primary. This causes the current i, in the primary to decrease, which in turn decreases the magnetizing force H according to Equation 2. The decreasing magnetizing force H in turn causes the flux density (B) to decrease in magnitude and the rate of change to reverse direction. This action reverses the polarity of all currents flowing in the secondary windings including the base drive winding. Base current 1,, becomes negative. This completely drives the transistor Q into cut-ofi' and at the same time I becomes positive and turns on transistor Q Which now experiences the same history as Q,.

From this point on it will take longer for the switching cycle to occur since the collector current of Q, and Q now have to demagnetize the iron core from the state left by Q or Q, respectively and remagnetize it in the direction of the collector current flow. The period of the switching rate is approximated by the following relationship.

T= switching period 1 )/frequency I 4 a constant to correct for square wave operation B saturation flux density in lines per square inch T=BSK K=4ANIE108 A and N are mechanical quantities and therefore are constant. E is the supply voltage and'at this point can be considered as being held constant.

This clearly illustrates that the period of oscillation T is a function of the flux density saturation point 8 By controlling in time when the flux saturation level 8 is reached, the period of oscillation can be controlled. Since the transformer has more than one secondary winding, a changing current can be introduced in a secondary winding opposing the magnetizing effect of the primary winding and thus controlling the magnetizing force H of the primary winding. This relationship can be expressed as:

H: l o) P H magnetizing force i= primary current i, secondary curren k NS/NP N secondary number of turns Np I primary number of turns While the transistors Q, or Q, are in saturation, i varies as a function of time. By supplying a cyclic secondary current, the sum of (i -1d,) controls the rate of change of H and this in turn controls the rate of change of B which determines when the pointof flux density saturation is reached. This, according to Equation 6, controls the period T.

The cyclic secondary current can be supplied from another oscillator. The oscillator can be a swing motor as already described, or canzbe of other electro-mechanical nature consisting of a mass suspended from a spring. To this mass is a coil attached which passes through amagnetic field in a manner analogous to a moving coil speaker. Upon applying current to the movable coil in'the magnetic field, the suspended mass and coil start accelerating in a direction determined by the sense of the applied current. When motion impedes, the magnetic field of the external magnet induces a current in the coil opposing the cause producing it (Lenzs Law). The cause in this case is the primary current i, and the opposing current is 1', (Equation 7).

As the coil and mass continue accelerating, the opposing self-generated current keeps increasing until external forces resulting from the expanded or compressed spring and/or the compressed gas in a compressor, counteract the force of the applied current through the coil. The external forces are now decelerating the coil and its mass, causing the self-generated current to decay. This cyclic current controls the rate of change of the magnetizing force according to Equation 7. When the magnetizing force drives the iron into saturation B, the inverter switches state as previously described and repeats the same chain of events in the opposite direction.

Thus the electromechanical oscillating load controls the period T of the inverter as shown in Equation 6. The mag nitude of the electromechanical oscillations is controlled by the available supply voltage to the transistors Q, and Q, or by the number of turns in the load drive windings and the collector of windings of the transistors. Increasing or decreasing the cross section of the magnetic material will only affect efliciency. In order to achieve high inverter efiiciency, the natural resonance of the inverter without its load shouldbe lower than the natural resonance frequency of the electromechanical system.

Lowering the supply voltage E does not afiect the syntonization of the inverter to the electromechanical resonance since the level of the forcing current and, therefore, the level of the opposing current, are reduced proportionately.

increasing or decreasing the supply voltage E only changes thejamplitude of all oscillatory events but not frequency syntonization. Thus, the electromechanical resonance load of the inverter controls the period of oscillation of the inverter exactly.

FIG. 5 shows another modified wiring diagram for this invention. Parts in FIG. 5 corresponding to FIG. 2 are indicated by the same reference characters with a prime appended. A saturating core transformer 30' has a primary winding 34' connected across a coil 510 of a normal non-saturating core transformer 512.

Transistors 62' and 64' have their base terminals connected with opposite ends of a base drive winding 40 of the transformer 30'. Other terminals of the transistors are connected across opposite halves of the coil 510 of the nonnal non-saturating core transformer 512. A center tap 522 of the coil 510 is connected with one side of a power source 526 and the other side of the power source 526 is connected to the emitter terminals of both of the transistors 62' and 64'.

connected with and operated by the swing motor, a feedback signal circuit from a coil of the swing motor to a coil of the transformer, a power source, and switching means in the oscillator operated by the transformer in response to the feedback signals to supply impulses of power from the power source to the swing motor in syntonization with the period of oscillation of the swing motor.

2. The electrical apparatus described in claim 1 characterized by the transformer of the electromagnetic oscillator including magnetic material in which the point of flux saturation in time, of the electromagnetic material, is controlled by selfgenerated feed back signals from a coil of the swing motor.

3. The electrical apparatus described in claim 1 characterized by the switching means of the electromagnetic oscillator having means for supplying bi-directional current to the swing motor for driving said motor with either unidirectional or bi-directional power supplied to the electromagnetic oscillator from said power source.

4. The electrical apparatus described in claim 1 characterized by the oscillator including a transformer having a core that is saturated by the feedback signals from the motor, the swing motor including a circuit supplied with current from the transformer and in which current changes constituting the feedback signals are generated by movement of the swing motor, said current changes controlling the time when the core saturation of the transformer occurs, the switching means of the oscillator also including two transistors connected with and controlled by the transformer for the purpose of amplification and inversion of power supplied to the oscillator for the purpose of supplying alternating current of syntonized frequency to the swing motor.

5. The electrical apparatus described in claim 1 characterized by the oscillator having a natural period of oscillation, when disconnected from the swing motor, of a frequency that is different from that of the swing motor, and said oscillator including means that syntonizes its oscillation to the natural frequency of the swing motor when connected with the swing motor to supply power thereto, the natural period of the oscillator under no load being preferably lower than the natural frequency of the swing motor.

6. The electrical apparatus described in claim 1 characterized by the circuit connecting said swing motor and said oscillator being limited to two electrical connections.

7. The electrical apparatus described in claim 1 characterized by the oscillator being inductively connected with the swing motor through the transformer for supplying electric power to the swing motor whereby the swing motor is isolated from direct connection with the power source.

8. The electrical apparatus described in claim 1 characterized by the swing motor having spring means that cooperate with the mass of moving parts of the motor to impart a natural frequency of oscillation to the motor, the oscillator transformer having a secondary winding that supplies pulsating current to the swing motor, means in the oscillator responsive to the saturation of the transfonner for imparting a natural noload frequency to the oscillator, the saturation of the transformer being influenced by feedback signals, that result from changes in the back EMF of the swing motor, to the secondary winding for snytonizing the frequency of the oscillator and that of the swing motor.

9. The electrical apparatus described in claim 9 characterized by the load being a reciprocating compressor driven by the swing motor in unison therewith, the moving parts of the compressor and the pressure of the gas compressed by the compressor cooperating with the spring means and moving parts of the swing motor to determine the natural frequency of the swing motor-compressor assembly.

10. The electrical apparatus described in claim 8 characterized by the transformer having primary windings through which current pulses, the switching means in the oscillator being connected with said primary windings and being operable to supply current selectively to the primary windings in opposite directions, the switching means being responsive to the saturation of the transfonner.

11. The electrical apparatus described in claim 10 characterized by the switching means including two transistors, each of which is connected with a center tap of the primary winding and with a different end of the primary winding, another secondary winding on the transformer across which the bases of the transistors are connected, each transistor being connected between the center of the other winding and a different end thereof to provide a base drive for each of the transistors, which drive is also responsive to saturation of the transform er, the source of power being connected on one side to the center of the primary winding and connected on the other side through the transistors to both ends of the primary winding of the transformer, and capacitors connected from the bases of the transistors to the center of the primary winding for supplying initial power for starting the oscillator and for transient suppression.

12. The electrical apparatus described in claim 1 characterized by the electromagnetic oscillator including elements that control the flux density which produces saturation of the transformer with time constants that impart a natural frequency to the oscillator.

13. The electrical apparatus described in claim 12 characterized by the elements that control the magnetic flux density including two windings inductively coupled with one another but electrically insulated from one another.

i t i t UNITED STATES PATENT OFFICE v CERTIFICATE OF CORRECTION Patent No. 3,659,968 I Dated May 2, 1972 I lnventofls) j John A. Thomas, Jr .et a1 It is certified that: error appears the above-identified patent and that said LettersPatenI: are hereby corrected as shown below? Column Bg'line 11 "claim" 9", should read claim 8 Signed and sealed this 7th da f November 1972.

(SEAL) I A'GteBt: I

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer 1 Commissioner of Patents FORM 1 0-1050 (10459) UscoMM-Dc 50376-P69 I I W (1.5. GOVERNMENT PRINTING OFFICE; I969 0-35533l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. Dated May 2, 1972 Inventor s JOhn A. ThOmaB, JIM, et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 11 "claim 9" should read claim 8 Signed and sealed this 7th day of November 1972,

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 'ORM USCOMM-DC 60376-P69 U 5. GOVERNMENT PRINTING OFFICE I (969 OS55-334 

1. Electrical apparatus including an electromagnetic oscillator including a saturating transformer, a swing motor, a load connected with and operated by the swing motor, a feedback signal circuit from a coil of the swing motor to a coil of the transformer, a power source, and switching means in the oscillator operated by the transformer in response to the feedback signals to supply impulses of power from the power source to the swing motor in syntonization with the period of oscillation of the swing motor.
 2. The electrical apparatus described in claim 1 characterized by the transformer of the electromagnetic oscillator including magnetic material in which the point of flux saturation in time, of the electromagnetic material, is controlled by self-generated feed back signals from a coil of the swing motor.
 3. The electrical apparatus described in claim 1 characterized by the switching means of the electromagnetic oscillator having means for supplying bi-directional current to the swing motor for driving said motor with either unidirectional or bi-directional power supplied to the electromagnetic oscillator from said power source.
 4. The electrical apparatus described in claim 1 characterized by the oscillator including a transformer having a core that is saturated by the feedback signals from the motor, the swing motor including a circuit supplied with current from the transformer and in which current changes constituting the feedback signals are generated by movement of the swing motor, said current changes controlling the time when the core saturation of the transformer occurs, the switching means of the oscillator also including two transistors connected with and controlled by the transformer for the purpose of amplification and inversion of power supplied to the oscillator for the purpose of supplying alternating current of syntonized frequency to the swing motor.
 5. The electrical apparatus described in claim 1 characterized by the oscillator having a natural period of oscillation, when disconnected from the swing motor, of a frequency that is different from that of the swing motor, and said oscillator including means that syntonizes its oscillation to the natural frequency of the swing motor when connected with the swing motor to supply power thereto, the natural period of the oscillator under no load beinG preferably lower than the natural frequency of the swing motor.
 6. The electrical apparatus described in claim 1 characterized by the circuit connecting said swing motor and said oscillator being limited to two electrical connections.
 7. The electrical apparatus described in claim 1 characterized by the oscillator being inductively connected with the swing motor through the transformer for supplying electric power to the swing motor whereby the swing motor is isolated from direct connection with the power source.
 8. The electrical apparatus described in claim 1 characterized by the swing motor having spring means that cooperate with the mass of moving parts of the motor to impart a natural frequency of oscillation to the motor, the oscillator transformer having a secondary winding that supplies pulsating current to the swing motor, means in the oscillator responsive to the saturation of the transformer for imparting a natural no-load frequency to the oscillator, the saturation of the transformer being influenced by feedback signals, that result from changes in the back EMF of the swing motor, to the secondary winding for snytonizing the frequency of the oscillator and that of the swing motor.
 9. The electrical apparatus described in claim 9 characterized by the load being a reciprocating compressor driven by the swing motor in unison therewith, the moving parts of the compressor and the pressure of the gas compressed by the compressor cooperating with the spring means and moving parts of the swing motor to determine the natural frequency of the swing motor-compressor assembly.
 10. The electrical apparatus described in claim 8 characterized by the transformer having primary windings through which current pulses, the switching means in the oscillator being connected with said primary windings and being operable to supply current selectively to the primary windings in opposite directions, the switching means being responsive to the saturation of the transformer.
 11. The electrical apparatus described in claim 10 characterized by the switching means including two transistors, each of which is connected with a center tap of the primary winding and with a different end of the primary winding, another secondary winding on the transformer across which the bases of the transistors are connected, each transistor being connected between the center of the other winding and a different end thereof to provide a base drive for each of the transistors, which drive is also responsive to saturation of the transformer, the source of power being connected on one side to the center of the primary winding and connected on the other side through the transistors to both ends of the primary winding of the transformer, and capacitors connected from the bases of the transistors to the center of the primary winding for supplying initial power for starting the oscillator and for transient suppression.
 12. The electrical apparatus described in claim 1 characterized by the electromagnetic oscillator including elements that control the flux density which produces saturation of the transformer with time constants that impart a natural frequency to the oscillator.
 13. The electrical apparatus described in claim 12 characterized by the elements that control the magnetic flux density including two windings inductively coupled with one another but electrically insulated from one another. 